Blood pressure (low) - hypotension

The heart pumps blood around the body through the blood vessels. Blood pressure is the amount of force the pumping blood exerts on the artery walls.

Blood pressure varies with the body’s needs#

Blood pressure is not fixed. It rises during physical exertion and can fall in extreme heat. Hypotension, or low blood pressure, means the pressure of the circulating blood is lower than normal, or lower than would be expected given the conditions.

However, ‘hypotension’ is a relative term. One person may have lower blood pressure than others of similar build yet be perfectly healthy.

Low blood pressure is only a problem when it has a harmful effect on the body. If the pressure is too low for that particular person, vital organs (especially the brain) may be starved of oxygen and nutrients. A large blood loss can cause a sudden drop in blood pressure, a state known as shock.

The most dramatic sign of a sudden, severe fall in blood pressure is loss of consciousness. More often, low blood pressure develops gradually over time.

How low blood pressure is measured#

Blood pressure is measured using a device called a sphygmomanometer. As a general guide, if the reading drops around 30 mmHg below a person’s usual level, this is considered hypotension.

Low blood pressure has many possible causes, including:

• The body’s response to heat, which shifts blood into the vessels of the skin and can lead to dehydration
• Addison’s disease, where the adrenal glands fail to produce enough of the hormones that help maintain blood pressure

Orthostatic (postural) hypotension#

When you stand up from sitting or lying down, the blood vessels normally tighten in response to gravity, which helps keep blood pressure steady.

In orthostatic hypotension, the blood vessels do not adjust properly to standing. Blood pressure is allowed to fall, causing light-headedness. Causes include an irregular heartbeat (heart arrhythmia) and disorders of the nervous system.

Symptoms of hypotension#

• Light-headedness when standing up from sitting or lying down
• Unsteadiness or dizziness
• Weakness or fatigue
• Blurred vision
• Fainting

Common causes of hypotension#

• Emotional stress, fear or pain (the most common causes of fainting)
• Dehydration, which reduces blood volume
• Blood donation
• Internal bleeding, such as a perforated stomach ulcer
• Blood loss from trauma, such as a deep cut or serious accident
• Pregnancy
• Medications, including those for high blood pressure, diuretics (which cause fluid loss), some treatments for depression, and some heart medications
• Allergic reaction to certain drugs or chemicals
• Some infections, such as toxic shock syndrome
• Heart disease, which can weaken the pumping action of the heart
• Some nervous system disorders, such as Parkinson’s disease and neuropathy
• Prolonged bed rest

Treatment depends on the cause#

Treatment is directed at the underlying cause. For example, the dose of an existing medication may need to be adjusted, or a bleeding stomach ulcer may need surgical repair.

If no specific cause can be found, medication may be used to raise blood pressure. In extreme cases, a lower-body pressure suit may be needed.

Key points#

• A large blood loss can cause a sudden drop in blood pressure (shock).
• The most dramatic sign of a sudden, severe fall in blood pressure is loss of consciousness.
• Common symptoms include light-headedness, dizziness, blurred vision and fainting.
• Causes range from dehydration and bleeding to certain medications and heart or nervous system conditions.
• Treatment depends on identifying and addressing the cause.

Where to get help#